(A) Field of the Invention
This invention relates to controlled speed, variable ratio drive systems using centrifugally operated variable diameter pulleys.
(B) Discussion of the Prior Art
Controlled speed accessory drives have been shown to be capable of improving the fuel economy of automobiles, but have not been widely adopted by automobile manufacturers due, among other reasons, to their high cost and lack of reliability. Typical of such prior art drives is the system disclosed in U.S. Pat. No. 3,981,205 wherein the accessories of an automobile are driven by a cooperating pair of variable diameter pulleys one of which is centrifugally operated to cause variation in its effective diameter dependent upon its rotation speed. Devices of this type permit automatic variation in the speed ratio between the engine and the driven accessories and can be designed to drive the accessories at a nearly constant speed approximating the optimum operating speed of the accessories irrespective of the speed at which the engine operates. Thus, even at the high engine speeds encountered during highway usage, only a portion of this engine speed is transmitted to the accessories. The engine power not used to drive the accessories contributes to increased fuel economy. For a more explicit general discussion of this subject, see "Controlled Speed Accessory Drive", copyright 1976 by Morse Chain Division, Borg Warner. Controlled speed drive systems of this type also have application in the drive trains of small motorized vehicles such as motor cycles, mini bikes and motor scooters whereby such systems operate as an automatic transmission having infinitely variable ratio between upper and lower limits, as disclosed, for example, in U.S. Pat. No. 3,747,721.
While known for the purposes noted above, available variable ratio drive systems employing centrifugally operated, variable diameter pulleys suffer design inadequacies which have impaired their widespread use. For example, a variable diameter pulley including a centrifugal operator is normally complicated in design, adds significantly to the space requirements of the pulley mechanism which it is designed to replace and requires frequent cleaning. More particularly, it is a basically recognized principle that the more working parts possessed by a mechanism, the greater will its chances be of experiencing a mechanical failure. The complicated design of known centrifugally operated pulleys generally include an operator mechanism axially positioned to one side of a pair of main pulley members thus requiring a casing or housing separate from the main pulley members. If the added expense of sealing this auxiliary housing is not undertaken, the operating surfaces of the mechanism must be left exposed to the atmosphere, thereby creating the possibility of decreased efficiency or failure due to atmospheric-borne contaminants normally found in and about engines. The inconvenience and/or expense of frequent cleaning necessarily results.
Yet another disadvantage of known variable ratio drive systems employing centrifugally operated variable diameter pulleys is the relatively large amount of space which such systems require. Particularly for small, modern vehicles designed for high fuel efficiency yet equipped with numerous accessories requiring direct engine drive such as a water pump, power steering, air conditioning and an electrical alternator, the problem of system size poses very real problems. Therefore, a controlled speed, variable ratio accessory drive which requires more space within the engine compartment than is occupied by conventional pulley systems is not an attractive system, regardless of its potential for increasing fuel efficiency.